Cyclical, start-stop process controllers employ clutch/brake units which are driven by electric motors. The output side of the clutch/brake unit drives a gear reducer. It is not uncommon for this type of device to start and stop 30-60 times per minute in a process control application. A conventional clutch/brake unit has an output shaft that has a keyed connection with the gear reducer it drives. The key transmits torque from the shaft to the gear reducer.
In order to allow installation, clearance is necessarily provided between the shaft and the bore in which it fits, and also between the key and the keyway. Because of the cyclical starting and stopping of the output shaft, the key pounds alternately against opposite sides of the keyway as the torque reverses. The clearance between the shaft and bore also results in enough play that the shaft and bore wall pound against one another. As a result of these cyclical impact forces, the key and keyway as well as the shaft and bore are subjected to undue stresses which can cause one or more of these parts to fail prematurely.